1. Field of the Invention
This invention relates to a system for positioning engraving heads, and more particularly, to engravers having multiple engraving heads and a system for automatically axially positioning engraving heads into alignment in a predetermined configuration relative to a cylinder to be engraved.
2. Description of Related Art
The electromechanical engraving of a gravure cylinder involves rotating a cylinder while actuating an engraving head, or engraving heads, having a diamond stylus carried on an oscillating shaft. The stylus cuts or engraves cells or lines into the surface of the cylinder to produce an engraved cylinder for use in a printing process. The engraved cylinder is normally used in a web-type gravure printing press for printing paper, plastic, metallic film material, or other printed material.
In engravers for engraving cylinders used for printing publications, such as magazines or the like, the engraver includes multiple engraving heads wherein each engraving head includes a diamond stylus. By providing multiple heads, each head may be used to engrave different portions of the cylinder simultaneously wherein each portion of the cylinder engraved by a respective head may, by way of example, correspond to a different page of a publication.
The movement of the styli for performing the engraving operation is precisely controlled to ensure that the engraved cells or lines formed by each engraving head are located at the desired positions on the cylinder. However, the initial positioning of the engraving heads relative to each other has historically been very labor intensive wherein a skilled worker manually adjusted the position of each engraving head prior to an engraving operation.
For example, in a prior art engraver, a carriage carrying a plurality of engraving heads was positioned at a specific axial location, relative to an axis of a cylinder to be engraved, and one of the engraving heads was manually positioned in an axial direction into predetermined alignment with a fixed reference point. Then the carriage was moved or indexed a predetermined distance from the reference point and the next head was manually positioned into predetermined alignment with the reference point. This procedure was repeated until all of the engraving heads were positioned. The prior art method for positioning engraving heads has proven to be time consuming and it is difficult to obtain repeatable accuracy in positioning the heads. Further, movement of one of the heads, such as may be required to replace a diamond stylus, requires that the positioning of the other heads on the carriage be checked and/or adjusted to ensure that the relative positioning from head to head is maintained.
Accordingly, there exists a need for a system for locating multiple heads used in an engraving operation wherein the heads may be quickly and easily set up in a predetermined configuration at predetermined positions. Further, there is a need for such a system wherein a predetermined set-up for the heads may be accurately and repeatably obtained.